The present invention is directed to a lithium-air battery having high capacity and recycle efficiency.
Lithium ion technology has dominated the market as energy source for small electronic devices and even hybrid electric vehicles. However, Li-ion batteries have insufficient theoretical capacity to be a power source for future high capacity generations of power sources capable to run an electric vehicle.
Metal-air batteries have been under investigation as an advanced generation of high capacity energy sources that have the potential to power vehicular devices for distances comparable to present hydrocarbon based combustion engines. In a metal-air battery, the metal of the anode is oxidized and the resulting cation travels to the cathode zone containing a porous matrix of a material such as carbon, for example, where oxygen is reduced and the reduction product as oxide or peroxide combines with the metal cation to form the discharge product. Upon charge, this process is ideally reversed. Metal-air batteries are recognized to have potential advantageous properties over metal ion batteries because the cathodic material, oxygen, may be obtained from the environmental air atmosphere and the capacity of the battery would in theory be limited by the anodic metal supply. Thus, oxygen gas would be supplied continuously from outside the battery and battery capacity and voltage would be dependent upon the oxygen reducing properties and chemical nature of the discharge product formed.
Lithium air batteries have the potential to supply 5-10 times greater energy density than conventional lithium ion batteries and have attracted much interest and development attention as a post lithium ion battery technology. For example, a nonaqueous lithium air battery which forms Li2O2 as discharge product theoretically would provide 3038 Wh/kg in comparison to 600 Wh/kg for a lithium ion battery having a cathodic product of Li0.5CoO2. However, in practice, the metal air technology and specifically current nonaqueous lithium air batteries suffer many technical problems which have prevented achievement of the theoretical capacity.
The capacity of the Li air battery is highly dependent upon the capacity of the cathode matrix to store the Li2O2 discharge product. Li2O2 is generally insoluble in conventional nonaqueous solvents employed in metal air batteries. Therefore, upon formation at the cathode matrix the Li2O2 precipitates and fills the surface porosity of the cathode matrix effectively preventing access to the vacant capacity of the matrix interior region. Moreover, Li2O2 is an insulator and once the surface of the matrix is coated, oxygen reduction is prevented and discharge terminated, i.e., the capacity of the battery is severely reduced in comparison to the theoretical capacity.
As indicated above, effort to address this problem and to produce an efficient high capacity lithium air battery has received much attention.
Christensen et al. (U.S. 2014/0087273) describes a lithium-air electrochemical cell constructed with a negative electrode, a positive air electrode and a porous reservoir (precipitation zone) spacially arranged between the two electrodes that is in fluid communication with the positive electrode such that discharge product formed during cell discharge is located within and precipitates in the reservoir. Christensen discloses a separator between the negative electrode and the reservoir and lists conventional electrolyte systems. Ionic liquids are not described. Also not described is a structure containing a solid state conductor which separates the system into a negative electrode compartment and a positive electrode compartment.
Zhang et al. (U.S. 2014/0072884) describes a lithium-air battery wherein the air cathode is separated from the lithium anode by a solid polymer electrolyte (SPE) containing a cross-linked polysiloxane membrane. The SPE may be formed directly on the anode, formed on a ceramic separator placed between the anode and air cathode or laminated with a second polymer. The problem Zhang addresses is to provide a less fragile separator that prevents lithium dendrites from growing to the cathode.
Eicher et al. (U.S. 2014/0045078) describes a lithium-air electrochemical cell containing a lithium metal anode and a conventional air cathode. The cell is divided into two compartments by a membrane which is ion specific. The electrolyte solvent of the cathode compartment may be organic or aqueous while a solvent is required for the anode compartment. The electrolyte contains lithium difluorophosphate and a fluorinated solvent. Eicher does not disclose or suggest an ionic liquid as a component of the electrolyte of the cathode compartment and does not disclose or suggest an electrolyte wherein the lithium ion concentration at the cathode is very low.
Samsung Electronics (U.S. 2014/0011101) describes a lithium-air battery having a lithium anode which is coated with a protective electrolyte layer followed by a lithium ion conductive solid electrolyte membrane (SEM). On the cathode side of the SEM is electrolyte and another separator separating the air cathode from the anode. This structure creates an anode compartment and a cathode compartment. However, Samsung does not disclose or suggest a cathode compartment electrolyte containing an ionic liquid and a low concentration of lithium ion near the cathode.
Christensen et al. (U.S. 2013/0330641) describes a lithium-air battery having a lithium anode separated from an air cathode. An electrolyte composition is located both at the cathode and within the separator. The air cathode conatins a lithium insertion material for retaining the lithium peroxide discharge product. The insertion material is coated with a polymer which is permeable to lithium ions but impermeable to the electrolyte. This reference does not disclose a compartment construction wherein the cathode compartment contains an ionic liquid and the concentration of lithium ion near the cathode is low.
Amine et al. (U.S. 2013/0230783) describes a lithium-air battery containing a generally standard construction of a lithium anode, a separator and a air cathode. In order to form nanocrystalline lithium peroxide the ether based electrolyte contains a polyalkylene glycol ether, a lithium salt and a compound which favors formation of lithium peroxide having a low charge overpotential, thus leading to nanocrystalline structure. Amine neither discloses nor suggests a cell of compartment construction wherein the cathode compartment contains an ionic liquid and the concentration of lithium ion near the cathode is low.
Nakanishi (U.S. 2010/0151336) describes a metal air battery (lithium-air battery is exemplified) which is constructed to maintain the volume of electrolyte at a constant value throughout charge and discharge cycles. This is accomplished by having a constant circulation of electrolyte through the cell and/or by actually monitoring the electrolyte level and adding electrolyte when the level is low. Nakanishi also describes admission of an inert gas to the cell to dilute the oxygen concentration. The construction of the Nakanishi cell is of a conventional format with the devices described above added.
Peled et al. (WO 2011/154869) describes a metal-air battery (sodium-air battery exemplified) constructed with an anode containing a molten metal within a porous framework coated with a solid electrolyte interphase film (SEI), an electrolyte system and an air cathode. Ionic liquids are described as electrolyte components. The SEI contains sulfur derivatives, metal salts and optionally polymer. Peled discloses a wide variety of electrolyte mediums including a ceramic membrane and a polymer electrolyte. Conventional high boiling organic solvents are also described. A compartment construction wherein the cathode compartment contains an ionic liquid and the concentration of lithium ion near the cathode is low is not disclosed or suggested.
Gordon et al. (WO 2008/133642) describes a metal-air battery (both lithium-air and sodium-air batteries are exemplified) containing a metal anode, an ion selective membrane and an air cathode. The ion slective membrane is permeable to metal ions but not electrolyte and shields the anode from the aqueous electrolyte of the cathode. The anode compartment formed by the ion-selective membrane may contain a nonaqueous solvent compatible with the metal. The metal oxide salt formed in the cathode compartment is generally soluble in the aqueous electrolyte. Gordon does not disclose or suggest a compartment construction wherein the cathode compartment contains an ionic liquid and the concentration of lithium ion near the cathode is low.
In spite of the significant ongoing effort there remains a need to develop and produce an efficient, safe, cost effective, high capacity lithium air battery useful especially for powering vehicles to distances at least equal to or competitive with current hydrocarbon fuel systems.